means A coastal wetland of low-lying ground regularly flooded by tides, dense with salt-tolerant grasses and grading between land and sea.

from A plain English compound, exactly what it says: "salt" (Old English sealt, the Germanic word for the stuff of the sea) plus "marsh" (Old English mersc, soft wet ground, a cousin of "mere," a body of standing water). Put together, a marsh that tastes of the tide — the name is as honest as the place.